Need Advice

You would know best if your g/f will not be comfortable with switching to a situation where she only fucks her fuck buddy stud and you get hand jobs. But given you see there is a risk she might not accept this, going slow with incremental steps would seem best. Also, after a while if he has not already insisted, it may be possible for you to ask the fuck buddy if he will persuade her to stop fucking you.

Seems to me you could keep fucking for now but in step with asking for hand jobs while she describes her sessions with her stud. As this happens more and more, comment on how much better her stud seems, how you are in awe etc, how you would wish to be more like him, emphasise how you admire him, respect him, and gradually feel much less of a man than him, and then unworthy to compete. At the same time be telling her how much you like your hand jobs, that you feel it is the best way for a male like you to get off, without the anxiety of competing with a stud. If she is submissive in her attitude to her stud fuck buddy, encourage this and as far as you credibly can (so she is not turned off) mimic this presentation to him.

If you take care and allow the situation to develop at her pace so she remains comfortable, you should eventually be able to persuade her to treat you to hand jobs only and she will see that as appropriate behaviour for a male like you. But you obviously need to ensure she remains content with her fuck buddy stud all this time. (Really envy your situation btw)